This invention relates generally to the conveyance of heavy loads such as cargo containers and pallets and, more particularly, to an apparatus and a method for pivoting or turning these loads while they are being conveyed.
In conveyance systems, it is often necessary to pivot conveyed loads such that the loads are presented with a particular orientation. Typically, these conveyance systems include a plurality of freely-rotating bearings for supporting the loads and a plurality of powered roller drive mechanisms for propelling the loads. These drive mechanisms are normally located below a conveyance plane defined by the support bearings, but have rollers which are selectively movable to a position proximate to the conveyance plane for frictionally engaging and propelling the loads. The powered roller drive mechanisms are generally fixed in orientation and are capable of propelling loads in either of two directions. In order that the loads may be automatically conveyed, the powered roller drive mechanisms are generally located at uniform intervals such that loads encounter a new drive mechanism's roller upon leaving an old one and thus experience continuity of motion. Likewise, the support bearings are generally uniformly distributed such that the loads are evenly supported by them.
An exemplary use of a conveyance system of this type is in the loading of heavy loads aboard an aircraft. A load positioned outside the cargo door is supported by freely rotating bearings on a system aligned with a conveyance system in the aircraft. A self-lifting, powered drive mechanism may be activated, lifting its roller into frictional engagement with the bottom surface of the load and then rotating so as to propel the load into the aircraft. In order that this frictional engagement may be provided, it is necessary that the drive mechanism apply a normal force to the load's bottom surface. The load, however, remains supported primarily by the support bearings. When inside the aircraft, the load is similarly supported by bearings and is engaged by self-lifting powered drive mechanisms which propel the load along a first conveyance path, further into the aircraft. When the load has been propelled sufficiently far into the aircraft, the drive rollers are deactivated and retracted below the plane of support formed by the bearings. A second set of self-lifting powered drive mechanisms then engages the load and moves it longitudinally within the aircraft, along a second conveyance path, to a position where it may be secured for flight. The second set of drive mechanisms typically is mounted with a fixed orientation perpendicular to that of the first set of drive mechanisms
In some instances, the load must have a particular orientation within the aircraft. For example, the load may have a shape that necessitates a particular orientation for optimal use of space. Also, aircraft cargo systems must handle oversized cargo pallets which weigh in excess of 25,000 pounds and which have greater lengths than either the aircraft door or the aircraft interior widths. Therefore, it is necessary to load these pallets lengthwise through the door and to pivot the pallets such that they may fit longitudinally within the aircraft's cargo hold.
Generally, in pivoting or turning loads in conveyance systems, a bar is used as a fulcrum for jostling the loads back and forth until the turn is complete. This method of pivoting the loads is both labor and time intensive. In addition, the fulcrum may dent or otherwise damage the loads, pallets or aircraft structure.
Some conveyance systems use instead rotatably-mounted power rollers or wheels. However, these often require a substantial amount of space below the conveyance plane, creating both undesirable design constraints and maintenance and cleaning problems. Frequently, the depth required for such a system's installation is unavailable or too costly to utilize. In addition, such systems do not provide for positive, safe control of the load.
It should therefore be appreciated that there is a need for a powered system for efficiently turning loads such as cargo and pallets which can be installed in existing conveyance systems without extensive alteration and which has a relatively low profile to facillitate maintenance and cleaning. The current invention satisfies this need and provides an efficient, useful conveyance system.